When you make the following dihybrid testcross MmPp x mmpp w

When you make the following dihybrid testcross MmPp x mmpp, what is your expected phenotype ratio when the genes are independently assorting and when they are linked?

Solution

When the genes are independently assorting, the phenotypic ratio is MmPp:Mmpp:mmPp:mmpp =1:1:1:1. The cross will be as follows

MmPp©mmpp

When the genes are linked, the alleles will not assort independently. The genes may be arranged in either of the two ways. Two dominant allele and two recessive alleles may be on the same chromosome. Duch an arrangement is called coupling. Also one dominant allele may be present on the same chromosome as one recessive allele and may be passed on together. Such an arrangement is called repulsion. The phenotypic ratio in either of the cases will never follow the phenotypic ratio of 1:1:1:1.